Countries With the Most Rainfall, and Why They Get So Much

The countries with the most rainfall are Colombia, which receives an average of 3,240 mm of precipitation a year, São Tomé and Príncipe (3,200 mm) and Papua New Guinea (3,142 mm), according to World Bank data for 2022. The rest of the top 10 are the Solomon Islands, Panama, Costa Rica, Samoa, Malaysia, Brunei and Indonesia, every one of them in the tropics. The figures are long-term national averages, which is why a country containing one of the wettest towns on Earth, India, does not come close.

Just outside the top 10 come Bangladesh (2,666 mm), Fiji (2,592 mm), Sierra Leone (2,526 mm) and Singapore (2,497 mm). Tuvalu, which earlier editions listed at 3,200 mm, has no figure in the 2022 release. At the other end of the same table, Egypt averages 18 mm and Saudi Arabia 59 mm. Four forces explain who sits at the top: the band of storms around the equator, mountains that force moist air upward, the small size of many of the wettest states, and seasonal monsoon winds.

The World Bank defines the figure as the long-term average depth of precipitation over the whole country, in space and time, and takes it from the UN Food and Agriculture Organization. Precipitation includes rain, snow and hail. Because it is an average over every square kilometre, the number rewards countries that are wet from end to end and punishes large countries with dry corners. The value also barely changes from year to year; it is a climate normal, not a record of how much fell in 2022.

That is why Colombia is remarkable. Only two countries in the top 10 cover more than a million square kilometres, Colombia (1.14 million km²) and Indonesia, and Colombia, unlike Indonesia, still averages more than 3 m of rain a year. Most of the others are islands or small states: São Tomé and Príncipe covers about 1,000 km², Samoa under 3,000 km² and Brunei under 6,000 km². Colombia manages its total because rain falls heavily on three of its fronts at once: the Pacific lowlands of Chocó, the Amazon basin in the southeast, and the rainforests of the Catatumbo in the northeast and the central Magdalena valley, while even its Andean slopes around 1,700 m receive 2,000 to 2,500 mm a year. Its genuinely dry land, the La Guajira Desert on the peninsula at the northern tip of South America, is the continent’s largest desert north of the equator, yet it covers too small a share of Colombia to drag the national figure down.

The Intertropical Convergence Zone over Colombia, Brunei and Indonesia

The first cause is latitude. Around the equator, the northeast and southeast trade winds meet in a band called the Intertropical Convergence Zone, or ITCZ. Solar heating drives air upward there in towering thunderstorms, and that rising air draws the trade winds in; sailors knew the calm belt as the doldrums. The ITCZ follows the sun north and south through the year, and its passage produces the wet and dry seasons of the tropics in place of summer and winter.

All ten lie within reach of the ITCZ or of its great Pacific branch, the South Pacific Convergence Zone, which stretches southeast from the warm pool of the western Pacific and is considered the largest and most important part of the whole system. Colombia’s rainy seasons are caused by it, and Brunei’s climate is described as more subject to the ITCZ than to the trade winds, with few or no cyclones. Indonesia, the world’s largest archipelagic state, sits astride the equator. Samoa has an equatorial climate with a main rainy season from November to April, though heavy rain can fall in any month.

Mountains that wring out the wind: Chocó, the PNG Highlands and São Tomé

Latitude sets the stage, but mountains decide where the heaviest rain lands. When moist ocean air is forced up a slope, it cools and its water condenses and falls. Colombia’s Pacific department of Chocó, where the Baudó Mountains on the coast and the Cordillera Occidental inland lift air coming off the Pacific, is described as the rainiest lowland in the world, with close to 10,000 mm a year. The town of Lloró recorded an average of 12,717 mm between 1952 and 1989 at an agricultural farm nearby, and López de Micay, farther south in Cauca, reported 12,892 mm a year between 1960 and 2012; both claims are disputed.

Papua New Guinea shows the same effect inside one country. Its winds blow from the southeast from May to October and from the northwest from December to March, and the central mountain spine turns them into wide local differences: some highland areas receive more than 8,000 mm a year, while Port Moresby, in a rain shadow, gets less than 1,000 mm. On São Tomé, annual rainfall ranges from about 7,000 mm in the highland cloud forests to about 800 mm in the northern lowlands. Its climate is shaped by southerly monsoon winds, the warm Guinea Current and its steep volcanic relief, which includes the 663 m plug of Pico Cão Grande. Costa Rica, whose rainy season runs from May to November, and Panama both have a mountain spine between two oceans; in Panama, rainfall ranges from under 1,300 mm to over 3,000 mm, and the Caribbean side is much wetter than the Pacific. Almost all of it falls in a rainy season that usually lasts from April to December. That rain has an economic job: the Chagres River, dammed at Gatun, forms Gatun Lake, the artificial lake that makes up part of the Panama Canal.

Small islands with no dry interior: the Solomon Islands, Samoa and Tuvalu

The third cause is geometry. A country that is all coast has no dry heartland to pull its average down. The Solomon Islands, a scattered archipelago east of New Guinea, have an ocean-equatorial climate that is extremely humid all year, with annual rainfall of about 3,050 mm and more frequent rain and squalls when northwesterly winds blow from November to April. Samoa and São Tomé and Príncipe are similar: volcanic islands where no point is far from warm sea.

Yet heavy rain does not guarantee enough water. Tuvalu, whose atolls typically receive 200 to 400 mm a month, relies on collecting rain from roofs as its main source of fresh water; only Nukufetau, Vaitupu and Nanumea have sustainable groundwater, and a desalination plant on Funafuti fills the gaps in dry spells. In Colombia, Quibdó, the capital of Chocó, has lacked safe drinking water despite its rain. Rainfall ranks climate, not water security.

Monsoons in Malaysia and Bangladesh

The fourth force is the monsoon, a seasonal reversal of wind that carries ocean moisture inland for months. Malaysia’s average annual rainfall is usually given as about 2,500 mm, and it faces two monsoons: the southwest monsoon from late May to September and the wetter northeast monsoon from October to March, which originates over China and the North Pacific. El Niño years reduce Malaysia’s dry-season rainfall, though a long-term average smooths such swings out. Kota Bharu in Kelantan received 608 mm in a single day on 6 January 1967, and Sandakan in Sabah recorded 5,687 mm in 2006, Malaysia’s wettest year on record. Bangladesh, 11th at 2,666 mm, receives the South Asian monsoon across the flat delta of the Ganges and Brahmaputra.

Why India, home of Mawsynram, averages only 1,083 mm

The clearest proof that size matters is India. Mawsynram, a town at about 1,400 m in the Khasi Hills of Meghalaya, 15 km west of Cherrapunji, is often called the wettest place on Earth, with an average of 11,872 mm a year. On 17 June 2022 it received 1,003.2 mm in 24 hours. Three things combine there. Warm, moist monsoon air moving north from the Bay of Bengal is squeezed into a narrow zone over the Khasi Hills; the hills run east to west, directly across its path, so the air is forced sharply upward and cools; and strong winds aloft keep pulling the lifted air up, so the rain barely stops for the whole monsoon season.

Yet India as a whole averages 1,083 mm, ranking 87th of 180 countries in the 2022 data, because the Thar Desert, the Deccan Plateau’s rain shadow and the cold heights of Ladakh are averaged in with Meghalaya. Brazil, which holds most of the Amazon rainforest, averages 1,761 mm for the same reason: the dry northeastern interior balances the wet basin. The United Kingdom, with its reputation for grey skies, averages 1,220 mm, more than India but less than half of Colombia. The same logic explains why the top 10 is so small and so tropical, and why it changes very little from one edition to the next.

For a closer look at how seasonal winds deliver this rain, see our explainer on how monsoons work; for Colombia’s five climate regions, from Chocó to the páramo, read our guide to the climate of Colombia.